Yb3+ Er3+ 이온에 의한 Up-converting 나노 형광체 연구 및 광촉매 응용

Abstract

In recent years, up-conversion (UC) phosphors have attracted a great deal of attention due to their potential applications in bio-labeling, as infrared light sensors, for laser cooling, and in white LED (light emitting diode). Decrease in the size of UC phosphor particles to the nano-scale, will extend their use to a wider range of applications from laser materials to nano-bio-labels, nano-lighting devices, and nano-display devices. The UC phosphor would be a good candidate for a new optical LED device due to its emission of the three primary colors depending on the doping ratio of Er3+ and Yb3+ ions. A UC phosphor can also be used as a solar catalyst in NIR quantum counters to increase solar-cell efficiency for energy storage. Insufficient intensity, however, still constitutes the main limitation for practical applications of nanosized UC materials. Compared with well-characterized bulk crystals, the UC emission in nanocrystals usually undergoes a more efficient nonradiative process and suffers from a lower efficiency, since sol-gel synthesis and hydrothermal synthesis methods induce surface contamination with high phonon energy and defects. In this thesis, two specific synthesis technicues and a new application of a UC phosphor were investigated. The first chapter deals with the highly condensed transparent UC phosphor bodies synthesized by the SPS technique for highly efficient UC characteristic. In the second chapter, UC nanocolloidal suspensions were fabricated by pulsed laser ablation of pure bulk target in liquid phase for a contamination-free product. Finally, in the third chapter, a new application of the UC process for photo-catalysis was introduced by using Yb, Er co-doped N-TiO2. In conclusion, a highly efficient UC phosphor was fabricated by SPS and the PLA technique that overcame the limited efficiency problem and extended the application areas of UC phosphors. The finding from this research will be useful for making nano phosphors and could be extended to numerous applications such as energy transformation and photo-voltaic systems.